1. Field of the Invention
The present invention relates to electrostatic monitoring devices for warning against atmospheric electrical gradients such as electrical storms; and more particularly, to a wearable lightning hazard device which detects and provides an audible warning in the event of approaching electrically charged thunderstorms with potential for lightning strikes.
2. Description of the Prior Art
People can be struck by lightning when they are involved in outdoor activities such as golfing, fishing and other recreational activities on an overcast day. It is difficult, from a practical standpoint, to predict lightning hazard potential since no visible clue is available to indicate the hazard. The presence of a nearby thunderstorm and lightning activity provides little or no indication concerning lightning hazard potential for individuals within the storm locus.
Various elements of high voltage and electrical charge detection methods are known in the art. These elements have found use in connection with detection schemes for signaling the approach of thunderstorms; detection of nearly proximate high tension wires to prevent shock hazard; detection of friction induced body charges which may damage electronic circuits; and protection of the wearer from accumulating excess static charge which may destroy electronic circuits.
U.S. Pat. No. 3,891,919 to Penninger discloses a storm lightning detector, which uses radio frequency signals emitted by the lightning flashes during a thunderstorm. Two AM receivers are tuned to different frequencies. A lightning flash concurrently generates noise in each of the AM receiver signals—a wide band transmission of noise—that is unlike other common AM disturbances. This disturbance created in two different AM frequencies is used to detect the presence of lightning. The closer the lightning flash is to the detector, the larger becomes the disturbance in the AM signals of the detector's receivers. A warning signal provided by the Penninger device is said to provide significant reaction time, since atmospheric disturbance produced by a lightning streamer travels several kilometers. While the Penninger device is useful for detecting far away lightning strikes, an imminent lightning strike is not detected until it has already occurred.
U.S. Pat. No. 5,057,820 to Markson et al. discloses an optical warning system. An optical detector identifies the presence of lightning or a strobe light from another aircraft, so that collision can be avoided. The strobe light is identified by its periodicity, while lightening is identified by its non-periodic behavior. Two or more detectors can localize the lightening or a strobe light. An RF detector may be added together with the optical system to verify the presence of lightening. The device is useful for identifying inter-cloud lightning even in bright daylight. This device is not adapted to be worn by the user. It detects lightning strikes after they occur and provides no detection against an imminent lightning hazard.
U.S. Pat. No. 5,263,368 to Breitmeier et al. discloses a hand-held lightning detection and ranging device. Radio frequency emissions from lightning are picked up by an antenna and filtered to select low frequency emissions. The filtered signal is compared against a standard to activate light emitting diodes that are said to indicate lighting disturbance at 0–10 miles distance and 10–20 miles distance. The frequencies utilized are 700 Hz, which represents a lightning disturbance of 10–20 miles distance, and 1400 Hz, which represents a 0–10 mile distance lightning disturbance. Breitmeier's device detects far-away lightning events. Detection of lightning strikes follows their occurrence. The Bregmeier device is incapable of detecting an imminent lightning strike hazard before it occurs.
U.S. Pat. No. 4,007,418 to Hanna discloses a personal electrostatic safety monitor having an induction plate sensing means. A plate isolated by two capacitors is connected to a positive preamplifier and a negative preamplifier. The leakage current and voltage are amplified to determine the rate of power dissipation so that a hazard potential can be established. High power dissipation rate is indicative of danger. Column 4 lines 10–12 of the Hanna patent describes use of the personal electrostatic safety monitor in atmospheric electrical gradients such as electrical storms. When high power dissipation is observed by the Hanna device, accumulation of negative charges is already substantial and will likely initiate a lightning strike, since the threshold value required by the device is based on the quantity of dissipation that is safe for humans to endure. Once this high charge value accumulates, a subsequent high voltage strike is probable owing to the state of charge accumulation. Consequently, any warning provided by the Hanna device arrives too late to avoid a lightning strike, which can even be initiated by the device, itself.
U.S. Pat. No. 4,714,915 to Hascal et al. discloses a portable electrostatic field safety monitor. The patent discloses a portable electrostatic field safety monitor for use by linemen who work on high voltage power lines. It provides an audible alarm when an electrostatic field beyond a set value is detected. An induction plate coupled to the AC current flowing through the power lines measures a DC voltage against a floating ground to detect the presence of high voltage in the power lines. Since the coupling process is inductive, the Hascal et al. device requires an AC field, which is not present in a thunderstorm. Accordingly, the Hascal et al. monitor provides no information concerning lightning hazards.
U.S. Pat. No. 4,983,954 to Huston discloses a shock hazard-warning device. A portable, wrist wearable, warning device becomes coupled with the AC signal transmitted by high-tension electrical wire. Detection of shock hazard potential created when the wearer approaches the high-tension wire is based on a threshold value set in the device. The Huston device is finely tuned, measuring line frequency via narrow band pass filters. It affords AC high voltage detection but cannot detect lightning hazard potential from a thunderstorm cloud.
U.S. Pat. No. 3,452,346 to Kupersmit, discloses a static charge detector, which uses two sets of circuitry to detect positive or negative charge. It uses a neon light to bleed the charges through a high resistance, thereby preventing damage to measurement circuits. The presence of high voltage generated current through two transistor circuits triggers an oscillator circuit, which produces an audible alarm. The Kupersmit patent discloses use of a single wire to collect positive or negative charges. Accordingly, the Kupersmit detector must be placed close to the charge source. It uses bleed circuits to protect the detection circuit from damage and detect the presence of static charge. The patent disclosure suggests no means for detecting the approach of rapidly moving negative charges. No disclosure is contained therein concerning means for warning a person of approaching lightning hazard.
U.S. Pat. No. 4,649,374 to Hoigaard discloses an electrostatic system monitor for determining electrostatic charge potential when assembling electronic IC circuits on a workbench. IC circuits are easily damaged by electrostatic charges, which cause arcing through the silicon oxide layers of the IC, damaging their functionality. The Hoigaard system monitors various operations in a workbench and alarms when electrostatic charge is excessive.
Several US patents to Campbell disclose a static monitoring system for IC fabrication. U.S. Pat. No. 4,785,294 to Campbell discloses that static monitoring is used to check whether the grounding wrist strap in an IC workbench station is properly grounded. The system also checks to determine whether an electrically charged ungrounded person is in dangerously close proximity to the work. An antenna determines whether electrically charged objects are in close proximity, and if so, causes the system to trigger an audible alarm. IC circuits are easily damaged by electrostatic charges. Such charges produce arcing through the silicon oxide layers of the IC, destroying circuit functionality. The system monitors the proper functioning of the ground strap in a work bench and signals an alarm when electrically charged objects moving close to the workbench have potential for applying to IC devices thereon a damaging electrostatic charge that would likely cause device failure. The Campbell device uses physical connections to sources of high voltage, an arrangement that cannot be used to detect approaching electrostatic charges signaling a lightning strike.
U.S. Pat. No. 5,359,319 to Campbell et al. discloses an electrostatic discharge detector and display. An electrostatic discharge in a circuit board, which is being assembled, results in a radio frequency radiation, which is remotely picked up by an electrostatic monitoring system. The system amplifies the antenna-received signal and displays it as a diode, indicating that electrostatic discharge was present during circuit board assembly. Electrostatic discharge is detected after it occurs; no suggestion is provided concerning detection of lightning hazard potential.
U.S. Pat. Nos. 5,461,369 and 5,463,379 to Campbell et al. disclose a wrist-wearable electrostatic discharge detector and display. An electrostatic discharge in a circuit board, which is being assembled, results in RF radiation. The RF radiation is remotely picked up by an electrostatic monitoring system. The system amplifies the antenna-received signal and displays it as a display in a wrist wearable device, indicating that electrostatic discharge was present during circuit board assembly. This wearable system detects electrostatic discharge after it has occurred, but does not detect lightning hazard potential.
U.S. Pat. No. 5,772,445 to Mousaa discloses an electrostatic meter. The device relies on a moving electrostatic field, creating an electromagnetic field, which can be picked up by a solenoid coil as an induced voltage. Disturbances in the electrostatic field are inductively picked up due to movement of charges. For the Mousaa device to work, the user must be very close to large amounts of rapidly moving charged particles. Such close proximity is required by the Maxwell's equations. It significantly diminishes the ability of the Mousaa device to detect charge accumulation from arriving negatively charged particles during onset of lightning activity.
U.S. Pat. No. 6,150,945 to Wilson (hereinafter the '945 patent) discloses a static charge-warning device. The device functions by examining the charge accumulated in two plates, which are separated from each other by a high impedance voltage-measuring device. Tribofriction results in charge accumulation on the body of a user, indicating differences in the potential of the separated plates. When the charge accumulation reaches sufficient magnitude, an alarm is sounded, advising the worker to discharge the accumulated charges before working on electronic IC components. The discharge function is accomplished by the Wilson device without initiation of an arc, so that charge accumulation problems are detected and resolved before electronic IC components become damaged. The Wilson patent thus discloses a warning device, which indicts that a person accumulates excessive charges. It discloses no means for discharging the accumulated charges. The Wilson device would not be suitable for detecting the arrival of negatively charged ions prior to a lightning strike, since voltage accumulated in the plates would greatly exceed the capability of the high impedance volt-meter Wilson uses to form the device's electronic circuit.
U.S. Pat. No. 3,745,412 to Ruff discloses an electrostatic discharge device, which enables a user to discharge static electricity, such as that picked up by walking, without applying an electric shock to the user. This discharge device does not detect arrival of electrostatically charged particles and is not a warning device for lightning hazard potential.
U.S. Pat. No. 5,457,596 to Yang discloses a static electricity protection wrist strap. A wrist-wearable static protection device helps to ground the wrist, thereby eliminating accumulated static charges so that circuit board assembly does not result in component failures. The unit senses variations in the capacitance of the skin with respect to a plate in the device, thereby determining the effectiveness of the grounding strap. The Yang device requires a physical connection to high voltage sources. It is not readily applicable to detection of impending lightning strikes.
There remains a need in the art for a wearable lightning hazard-warning device that indicates a lightning strike hazard potential based on charge accumulation, before the charge accumulation measurement itself triggers a lightning strike.